1915.] NATURAL SCIENCES OF PHILADELPHIA. 395 



fading to white around the umbihcus and on both sides of the chestnut- 

 brown shoulder band. 



The surface is glossy, lightly marked with growth lines, and 

 under a strong lens showing impressed spiral lines on the upper 

 surface of the last whorl (lacking, however, in many individuals). 

 Initial | whorl radially rippled, granulation then beginning, the last 

 f whorl having close protractively spiral threads, the intervals densely 

 wrinkled radially. Spire very low conic. Whorls 4f, the last 

 descending in front. The aperture is rounded oval; peristome 

 narrowly expanding, inconspicuously brown-edged, slightly thickened 

 within, the margins converging, joined by a thin, brownish-edged 

 parietal callus. 



Alt. 14, diam. 23 mm.; umbilicus 2.6 mm.; aperture 12 x 13 mm. 



Genitalia (PI. XII, figs. 1-3, 5, 5a). — The penis is small and slender, 

 at the base enclosed in a short but thick sheath. Penis-papilla 

 cylindric, more than half the length of penis, tapering distally to a 

 blunt or a somewhat pointed end. Retractor muscle inserted on 

 the epiphallus near its base. Epiphallus as long as the penis or 

 somewhat longer, terminating in a minute, bud-like flageUum. Lower 

 part of the vas deferens large, its diameter equal to or exceeding that 

 of the epiphallus. Vagina usually about twice the length of the 

 penis. 



Santa Rita Mountains, the type from Station 5, Walnut Branch 

 of Agua Caliente Canyon, at about 6,000 feet, with *S. santaritana 

 and S. clappi, type No. 112,164, A. N. S. P., collected by Ferriss, 

 Daniels and Pilsbry, 1910. Also taken at Station 3, "Soldier Can- 

 yon," at about 4,500 feet, and in Madera Canyon at Stations 7, 8 

 and 15. 



This fine species, named for Dr. Bryant Walker, is not uncommon, 

 though less generally distributed than S. santaritana. In the type 

 locality it lives with *S. santaritana and *S. clappi, sometimes all under 

 the same rock, sometimes in separate rock piles. The smallest 

 specimens, Station 5, measure 20 mm. in diameter; the largest, 

 Station 15, 24.3 mm. 



Station 3 is in a small canyon running in north of the mouth of 

 Agua Caliente, opening to the mesa between two high granite crags. 

 The rock is a coarse granite, and shells are not numerous. A single 

 giant cactus growing here is further east than we have seen the 

 species elsewhere. 



Many specimens have been dissected. The slender, short penis, 

 with a short, thick basal sheath, and the enlarged free vas deferens 



